Stormwater Quality at La Farge Library

Water quality measurements were taken at four locations near the La Farge Library on December 14, 2012.  Snow showers passed through Santa Fe over the course of the day.  Plowing was not necessary so it is believed that deicing salts on the streets were remnant from a larger snowstorm that fell on the area five days earlier on December 9th.  Measurements of pH, temperature, and total dissolved solids were taken between 3:30-4:00pm.  Photos of the measurement locations can be found below.

 

Location

pH

Temperature (Celsius)

Total Dissolved Solids (ppm)

Bio-retention Basin to West of La Farge Parking Lot

8.8

2.2

47

West Branch of the Arroyo de los Pinos

8.7

2.7

400

South Branch of the Arroyo de los Pinos (Below Llano Street Crossing)

8.4

2.9

220-260*

Llano Street Runoff (Immediately before dropping into Arroyo de los Pinos Storm Drain)

8.4

2.9

484

 *TDS measurements at the south branch of the Arroyo de los Pinos were fluctuating rapidly.  This was probably a result of water that hadn’t fully mixed with the Llano Street storm drain runoff about 50 feet upstream.

Small sample sizes preclude statistical comparisons, but obvious differences in water quality did exist for the four locations, particularly with respect to total dissolved solids.  The higher pH measurements for the bio-retention basin and the west branch of the Arroyo de los Pinos could be explained by greater buffering from more alkaline soil.  Runoff from Llano Street is predominantly from asphalt or concrete structures which could mean that the snow retains more of its natural acidity from a lack of interaction with local soils.  The Llano Street drain feeds into the south branch of the Arroyo de los Pinos immediately above where channel measurements were taken.  This could explain why the pH measurements were identical for these two locations.

The low water temperature in the bio-retention basin is probably due to shallow, non-flowing water being giving the opportunity to mix with colder air temperatures.  The water in the basin also originated from parking lot runoff  devoid of deicing salts.  The other three measurement locations clearly had greater salt contents as evidenced by their elevated TDS measurements.  It would appear that the west branch of the Arroyo de los Pinos drains from a predominantly impervious surface high in salts whereas the south branch mixed with more fresh water.

Click on sampling site photos to enlarge.